The present invention relates to a repetitive striking type nail gun, and more particularly, to a pneumatically operated nail gun for repeatedly striking, with a drive bit, fasteners such as nails and staples by repetitive reciprocation of a piston during pulling of a trigger.
Throughout the specification, expressions such as "upward," "downward," "above," "below," "upper" and "lower" are used in explanations of conventional art and the present invention to define the various parts when a nail gun is disposed in an orientation for driving a nail downward into a workpiece.
A conventional pneumatically operated repetitive striking type nail gun is disclosed in a Japanese Patent Application Kokai (OPI) No. Hei-2-172682. As shown in FIG. 7, the nail gun includes a main body 101, a handle 136 connected to the main body 101, an exhaust cover 102 provided to the upper portion of the main body 101, and a tail cover 112 provided to a lower portion of the main body 101. A drive air chamber 103 is defined in the main body 101 and the handle 136. The drive air chamber 103 is fluidly connected to a compressed air source (not shown), so that a compressed air is filled in the drive air chamber 103.
Within the main body 101, a cylinder 109 is provided, and a piston 110 is reciprocally and slidably disposed in the cylinder 109. A lower end of the cylinder 109 is in abutment with the lower portion of the main body 101. The piston 110 is integrally provided with a drive bit 111 extending in an axial direction of the cylinder 109.
A generally cylindrical return chamber 104 is defined between the main body 101 and the cylinder 109. At a lower peripheral portion of the cylinder 109, a plurality of return holes 124 are formed, so that the return chamber 104 and the cylinder 109 can be fluidly connected together. Further, at an axially intermediate portion of the cylinder 109, a plurality of communication holes 117 are formed. Radially outer ends of the communication holes 117 are covered by a flexible one-way valve 123, so that air in the cylinder 109 can be discharged toward the return chamber 104 through the communication holes 117, but air in the return chamber 104 cannot be flowed into the cylinder 109 through the communication holes 117.
At a position immediately above the communication holes 117, a first annular flange portion 109A is provided at an outer peripheral surface of the cylinder 109. Further, at the upper portion of the cylinder 109, a second annular flange portion 109B is provided.
A trigger 118 is pivotally movably supported to the main body 101, and a trigger valve 119 is retained in the main body 101. The trigger 118 is abuttable on the trigger valve 119 upon pivotal movement thereof for actuating the trigger valve 119. That is, if the trigger 118 is pulled upwardly, the trigger valve 119 is actuated so that compressed air in an upper head valve chamber 107 (described later) can be discharged to the atmosphere through the trigger valve 119.
In the tail cover 112, a fastener such as a nail can be supplied. Further, a push lever 120 is movably guided by the tail cover 112. The push lever 120 has a lower end in contact with a workpiece surface, and has an upper end engageable with the trigger 118. The upper end of the push lever 120 is normally biased downwardly by a spring 137 interposed between the main body 101 and the upper end of the push lever 120, so that the push lever 120 can provide a locking position of the trigger 118. On the other hand, if the entire tool is pressed downwardly, the workpiece surface pushes the lower end of the push lever 120 upwardly against the biasing force of the spring 137 for releasing the locking state of the trigger 118. The drive bit 111 is extendible into and is guided by the tail cover 112 upon downward movement of the piston 110 for striking the head of the nail supplied in the tail cover 112.
A head valve 105 is slidably disposed relative to the exhaust cover 102 and at a position between the exhaust cover 102 and the upper end of the cylinder 109. The head valve 105 is biased in the axial direction of the cylinder 109 downwardly by a head valve spring 126 interposed between the head valve 105 and the exhaust cover 102, so that the head valve 105 can be seated on the upper open end of the cylinder 109. Further, the upper head valve chamber 107 is defined between the exhaust cover 102 and the head valve 105. The head valve 105 is formed with an air passage 125 which provides fluid communication between the drive air chamber 103 and the upper head valve chamber 107. Further, an exhaust valve 121 is defined at the upper portion of the head valve 105 for discharging compressed air in the cylinder 109 and above the piston 110 when the head valve 105 is moved downwardly.
At a lower surface of the exhaust cover 102, a cylindrical recess is formed for defining a cylindrical repetitive valve chamber 108 in which a repetitive valve 106 is movably provided. An upper surface of the repetitive valve 106 serves a pressure receiving surface whose area is greater than that of the lower surface of the repetitive valve 106. The repetitive valve 106 divides the repetitive valve chamber 108 into a lower repetitive valve chamber 127 and an upper repetitive valve chamber 128.
Further, in the exhaust cover 102, an air passage 114 connecting the upper head valve chamber 107 with the lower repetitive valve chamber 127 is formed. A cross-sectional area of the air passage 125 formed in the head valve 105 is sufficiently smaller than that of the air passages 114 and another air passage 115 (described later). One open end of the air passage 114 faces the lower surface of the repetitive valve 106.
Between the exhaust cover 102 and the second flange 109B of the cylinder 109, a spacer or a cylinder guide 122 is fixedly positioned. More specifically, a packing 131 is provided between the exhaust cover 102 and the upper end of the main body 101. The cylinder guide 122 has an upper end 122A in abutment with the packing 131, a sleeve portion 122B extending along the inner peripheral surface of the main body 101, and a lower portion 122C in abutment with the second flange portion 109B of the cylinder 109. With this arrangement, an axially movement of the cylinder 109 can be prevented by the abutment between the lower portion 122C and the second flange 109B. More specifically, if the cylinder guide 122 is not provided, the cylinder 109 may be vibrated in its axial direction at every reciprocation. As a result, air inlet opening area between the upper open end of the cylinder 109 and the head valve 105 may be varied, so that the pressure applied to the cylinder 109 and above the piston 110 becomes changed at every striking operation. Accordingly, the nail cannot be desirably driven into the workpiece. To avoid this problem, the above described spacer or the cylinder guide 122 is provided to avoid axial movement of the cylinder 109.
Further, a radially inward annular projection 113 is provided integrally with the main body 101 at a position in contact with the first flange 109A. This annular projection 113 serves as a partition member for partitioning the return chamber 104 from the drive air chamber 103.
Further, the air passage 115 is provided for fluidly connecting the lower repetitive valve chamber 127 with the trigger valve 119. Thus, the air passages 114 and 115 provide a fluid communication between the upper head valve chamber 107 and the trigger valve 119 provided that the repetitive valve 106 maintains its upper position. Furthermore, an elongated air passage 116 is provided in the main body 101 for fluidly connecting the upper repetitive valve chamber 128 with the return chamber 104.
In operation, if the lowermost end of the push lever 120 is pressed against the workpiece, the uppermost end of the push lever 120 releases the lock of the trigger 118. With this state, if the trigger 118 is pulled upwardly, the upper head valve chamber 107 is brought into communication with the atmosphere through the air passage 114, the lower repetitive valve chamber 127, the air passage 115 and the trigger valve 119. Therefore, the compressed air in the upper head valve chamber 107 is discharged to the atmosphere out of the trigger valve 119.
Accordingly, the head valve 105 is moved upwardly, so that the upper open end of the cylinder 109 is opened. Consequently, driving air in the drive air chamber 103 is flowed into the cylinder 109 and rapidly urges the piston 110 downwardly. Because the drive bit 111 is provided integrally with the piston 110, the nail in the tail cover 112 is driven into the workpiece.
In this downward stroke of the piston 110, the air in the cylinder 109 and below the piston 110 is flowed into the return chamber 104 through the return hole 124, and is compressed in the return chamber 104. Further in the downward stroke, if the piston 110 moves past the communication hole 117, the compressed air in the cylinder 109 and above the piston 110 is also flowed into the return chamber 104 through the communication hole 117.
The compressed air flowed into the return chamber 104 will be flowed into the upper repetitive valve chamber 128 through the air passage 116. In this state, because atmospheric pressure is applied in the lower repetitive valve chamber 127 through the trigger valve 119 and the air passage 115, the repetitive valve 106 is urged downwardly so that the repetitive valve 106 is seated on the open end of the air passage 114. Thus, fluid communication between the air passages 114 and 115 is shut off. That is, the upper head valve chamber 107 is shut off from the atmosphere.
Because the upper head valve chamber 107 is communicated with the drive air chamber 103 through the air passage 125, application of the compressed air in the drive air chamber 103 into the upper head valve chamber 107 will increase pneumatic pressure in the upper head valve chamber 107 and in the air passage 114. Here, the lower surface of the repetitive valve 106 has a pressure receiving area smaller than that of the upper surface of the repetitive valve 106, and therefore, the repetitive valve 106 maintains its downward position for a given period, i.e., the communication between the air passages 114 and 115 is maintained in shut off state in spite of the pressure increase in the upper head valve chamber 107.
In accordance with the increase in pneumatic pressure in the upper head valve chamber 107, the head valve 105 is moved downwardly in cooperation with the biasing force of the head valve spring 126, and as a result, the head valve 105 is seated on the upper open end of the cylinder 109, whereby fluid communication between the drive air chamber 103 and the cylinder 109 is blocked. At the same time, compressed air in the cylinder 109 and above the piston 110 is discharged to the atmosphere through the discharge valve 121, because the discharge port is opened upon downward movement of the head valve 105. Accordingly, the piston 110 can be returned to its original top dead center position because of the application of the compressed pressure to the cylinder 109 and below the piston 110 from the return chamber 104 through the return hole 124.
The compressed air in the return chamber 104 is also discharged to the atmosphere through the minute gap between the drive bit 111 and the tail cover 112. Further, because of the expansion of the compressed air, the pneumatic pressure in the return chamber 104 is lowered, and therefore, the pressure applied to the upper repetitive valve chamber 128 through the air passage 116 is also lowered. Accordingly, the repetitive valve 106 is moved upwardly because of the pressure applied to the lower repetitive valve chamber 127 from the upper head valve chamber 107.
By the upward movement of the repetitive valve 106, the head valve chamber 107 is brought into communication with the atmosphere through the air passage 114, the lower repetitive valve chamber 127, the air passage 115 and the trigger valve 119. Thus, the compressed air in the upper head valve chamber 107 and in the air passage 114 can be discharged to the atmosphere out of the trigger valve 119.
Because the cross-sectional area of the air passage 125 is sufficiently smaller than that of the air passages 114 and 115, compressed air flowing amount into the upper head valve chamber 107 from the drive air chamber 103 through the air passage 125 is smaller than the air discharge amount from the upper head valve chamber 107 to the atmosphere through the air passages 114, 115 and the trigger valve 119. As a result, pressure in the upper head valve chamber 107 is rapidly lowered.
Thus, the head valve 105 is again moved upwardly to introduce the driving air in the drive air chamber 103 into the cylinder 109 to perform second striking or driving operation. The above described operation is consequentially and repeatedly performed so that the nail is subjected to repeated striking by the drive bit 111 as far as the trigger 118 is maintained in its pulling state.
With the conventional arrangement, the air passage 116 largely extends through the main body, and therefore, large machining area results. Further, since the radially inward annular projection 113 is provided integrally with the main body 101. Therefore, the radially inward annular projection 113 may become an undercut in die-casting or injection molding process. Therefore, the main body 101 would not be available as the die-casting molding product.
To avoid this problem, as shown in FIG. 8, a separate partitioning piece 213 can be hermetically provided at the hollow cylindrical space between a main body 201 and a cylinder 109. However, a fixing member such as a stop washer 240 is required for fixing the position of the separate partitioning piece 213.
Further, instead of the radially inward annular projection 113 provided to the main body 101, a corresponding partitioning segment can be integrally provided to the outer peripheral surface of the cylinder 109 at a position corresponding to the first annular flange 109A. However, in the latter case, the radially outward protruding length of the partitioning segment becomes large. Therefore, an original crude cylinder before machining must provide a large diameter, and machining labor is also increased, to degrade productivity.